7.3.2.2 Protocol Walk-through

7.3.2.2 Protocol Walk-through

While BGP provides support for quite complex routing policies (as an
example see Section 4.2 in [ROUTE:5]), it is not required for all BGP
implementors to support such policies. At a minimum, however, a BGP
implementation:

SHOULD allow an AS to control announcements of the BGP learned
routes to adjacent AS's. Implementations SHOULD support such
control with at least the granularity of a single network.
Implementations SHOULD also support such control with the
granularity of an autonomous system, where the autonomous system
may be either the autonomous system that originated the route,
or the autonomous system that advertised the route to the local
system (adjacent autonomous system).

SHOULD allow an AS to prefer a particular path to a destination
(when more than one path is available). Such function SHOULD be
implemented by allowing system administrator to assign weights
to Autonomous Systems, and making route selection process to
select a route with the lowest weight (where weight of a route
is defined as a sum of weights of all AS's in the AS_PATH path
attribute associated with that route).

SHOULD allow an AS to ignore routes with certain AS's in the
AS_PATH path attribute. Such function can be implemented by
using technique outlined in (2), and by assigning infinity as
weights for such AS's. The route selection process must ignore
routes that have weight equal to infinity.